Nanostructuring of bulk materials has led to significant improvements in the thermoelectric figure of merit, ZT, through the introduction of phonon scattering interfaces and energy-dependent scattering of carriers.1While valuable, these advances have typically required complex materials fabricated using energy-intensive, high-temperature, expensive processing methods. Here, the benefits of nanostructuring in high performance thermoelectric materials are realized in solution-processable polymer-inorganic composite materials. Cooperative transport combining the large Seebeck coefficient of colloidal inorganic Tellurium (Te) nanocrystals and the very high electrical conductivity of a conjugated polymer results in a composite material with an amplified thermoelectric power factor S2σ while retaining polymeric thermal conductivity. Our measured ZT˜0.2 is the largest reported value of ZT for a material processed entirely from water, and the largest reported in an organic or organic/inorganic composite to date. Currently there is no approach to producing stable, high performance solution processable thermoelectric materials.
Recently, there has been considerable focus on development of solution-processable optoelectronic materials, driven by substantial reductions in processing and manufacturing costs enabled by high throughput, large area processes such as spray coating and printing.2 Despite this active body of research, there has been little focus on developing these tools for thermoelectrics, a class of energy conversion devices with high module processing costs.
In response to this, focus on the thermoelectric transport properties of soluble conjugated molecules and colloidal quantum dots has intensified, however neither system alone seems capable of achieving stable, competitive values of ZT due to their intrinsic transport properties.3 In the case of conducting polymers, volatile doping techniques result in high electrical conductivities but low thermopowers.3a,d,f In the case of nanocrystals, high thermopowers have been reported, but high electrical conductivities have only been achieved using high temperature post processing at the expense of thermopower.4 In both of these established classes of solution-processable electronic materials, there exists no obvious strategy to stably improve the intrinsic power factor of either system, limiting the applicability of either one, individually, as thermoelectric materials. Recently, all organic composites of carbon nanotubes and conjugated polymers have demonstrated intriguing composite properties, but a maximum ZT of only 0.02.5 